﻿using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;

namespace TSharp.Core.Repository
{
    internal static class A
    {
        public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string property)
        {
            return ApplyOrder<T>(source, property, "OrderBy");
        }


        public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> source, string property)
        {
            return ApplyOrder<T>(source, property, "OrderByDescending");
        }


        public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string property)
        {
            return ApplyOrder<T>(source, property, "ThenBy");
        }


        public static IOrderedQueryable<T> ThenByDescending<T>(this IOrderedQueryable<T> source, string property)
        {
            return ApplyOrder<T>(source, property, "ThenByDescending");
        }


        private static IOrderedQueryable<T> ApplyOrder<T>(IQueryable<T> source, string property, string methodName)
        {
            string[] props = property.Split('.');
            Type type = typeof(T);
            ParameterExpression arg = Expression.Parameter(type, "x");
            Expression expr = arg;
            foreach (string prop in props)
            {
                // use reflection (not ComponentModel) to mirror LINQ 

                PropertyInfo pi = type.GetProperty(prop);
                expr = Expression.Property(expr, pi);
                type = pi.PropertyType;
            }

            Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), type);

            LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);

            object result = typeof(Queryable).GetMethods().Single(method => method.Name == methodName
                                                                             && method.IsGenericMethodDefinition
                                                                             && method.GetGenericArguments().Length == 2
                                                                             && method.GetParameters().Length == 2)
                .MakeGenericMethod(typeof(T), type)
                .Invoke(null, new object[] { source, lambda });

            return (IOrderedQueryable<T>)result;
        }

        //上面的代码满足所有的排序功能了，我的项目中只需要对单列排序，所以对代码做了简化


        /// <summary>
        /// 
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source"></param>
        /// <param name="property">排序字段</param>
        /// <param name="isAscdening"></param>
        /// <returns></returns>
        private static IOrderedQueryable<T> ApplyOrder<T>(IQueryable<T> source, string property, bool isAscdening)
        {
            Type type = typeof(T);

            ParameterExpression arg = Expression.Parameter(type, "x");

            Expression expr = arg;


            PropertyInfo pi = type.GetProperty(property);

            expr = Expression.Property(expr, pi);

            type = pi.PropertyType;


            Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), type);

            LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);


            object result;

            if (true == isAscdening)
            {
                result = typeof(Queryable).GetMethods().
                    Single(method => method.Name == "OrderBy" && method.IsGenericMethodDefinition
                                     && method.GetGenericArguments().Length == 2 && method.GetParameters().Length == 2).
                    MakeGenericMethod(typeof(T), type)
                    .Invoke(null, new object[] { source, lambda });
            }

            else
            {
                result = typeof(Queryable).GetMethods().
                    Single(method => method.Name == "OrderByDescending" && method.IsGenericMethodDefinition
                                     && method.GetGenericArguments().Length == 2 && method.GetParameters().Length == 2).
                    MakeGenericMethod(typeof(T), type)
                    .Invoke(null, new object[] { source, lambda });
            }

            return (IOrderedQueryable<T>)result;
        }
    }
}